Influenza Vaccination Implementation and Timing for Sri Lanka: A Cost-Effectiveness Analysis

Influenza causes an estimated 3 to 5 million cases of severe illness annually, along with substantial morbidity and mortality, particularly among low and middle-income countries (LMICs). The most effective way to decrease the burden of influenza is vaccination. Currently, Sri Lanka has no influenza vaccination policies and does not offer vaccination within the public healthcare sector. Therefore, a cost-effectiveness analysis of influenza vaccine implementation for the Sri Lankan population was performed. A static Markov model that did not account for transmission dynamics was used for this study. The model followed a theoretical cohort of Sri Lankans from all ages through two potential scenarios: universal influenza vaccination and no influenza vaccination across twelve-monthly cycles. Cost-effectiveness was analyzed using a governmental perspective at the national level. Costs for the study were broken down into three categories: direct, indirect, and vaccine costs. All costs were identified from previous literature for the local context. Vaccine efficacy was expressed as a range (48% to 72%) identified from a previous meta-analysis investigating similar settings. One model arm was considered cost-effective if the ICER was below a three-fold gross domestic product (GDP) per capita per DALY averted limit and highly cost-effective if below a one-fold GDP per capita per DALY averted limit. Utilizing TreeAge Pro software, we conducted both probabilistic sensitivity analyses and one-way sensitivity analyses for all model variables. The vaccination model arm reduced all influenza outcomes by approximately 60% (170,283 episodes, 3,167 hospitalizations, and 152 deaths) compared to no vaccination. By implementing vaccination earlier in the year, this reduction in the influenza disease burden was maximized. Vaccination was considered cost-effective compared to no vaccination, with a base case incremental cost-effectiveness ratio (ICER) estimated at Rs. 968,071.45 /DALY (5,418.62 USD/DALY). Sensitivity analysis identified that the ICER was sensitive to implementation month, monthly probability of contracting influenza, cost of vaccination, and years of life disabled. Due to only considering a one-year period, the implementation month had the most substantial effect on the ICER because no potential rollover effects of vaccination could be seen for the later implementation months. Probabilistic sensitivity analyses were performed on all variables, and there was a 99% probability that vaccination was cost-effective below a WTP threshold of 1,157,047.92 Rs/DALY (6,476.38 USD/DALY). No value for a variable within our estimated ranges resulted in ICERs above the WTP threshold of Rs. 2,066,157 (USD 11,556) per DALY averted. In conclusion, vaccination was considered cost-effective when compared to the implementation of no vaccine. However, due to a lack of national data, large-scale national studies are needed to determine better the influenza disease burden, at-risk population, and implementation cost.